1. Technical Field
This invention relates generally to the field of cable television systems and, more particularly, to method and apparatus for providing a reverse radio frequency transmission path from a CATV subscriber to a headend for reporting pay per view and other transactions in a CATV interdiction system.
2. Description of the Relevant Art
The cable television industry has recently resorted to look for new technology and to take a second look at technology developed in the early stages of development of cable television including negative and positive trap technology and interdiction systems to remove equipment off the subscriber's premises. The Scientific Atlanta CATV interdiction system, described by U.S. Pat. No. 4,912,760, evidences one product manufacturer's response to such concerns. Precipitating the removal of equipment from the subscribers' premises has been the provision of television channel conversion equipment within the new television receivers sold today and the predominance of so-called cable ready receivers. In other words, the converter portions of converter/decoders are in many instances no longer required. Also, removal of equipment from the subscribers' premises accomplishes a removal of equipment from the hands of pirates. The interdiction system described by U.S. Pat. No. 4,912,760 promotes the removal of all CATV equipment from a CATV service subscriber's premise except for equipment for certain special service applications such as pay per view services.
Most embodiments promoted by manufacturers of interdiction systems consist of a pole-mounted or side of building mounted enclosures located outside the subscriber's premises designed to serve four or more subscribers. This enclosure contains at least one microprocessor controlled oscillator and switch control electronics to secure several television channels. Control is accomplished by injecting an interfering or jamming signal into unauthorized channels from this enclosure.
In the Scientific Atlanta system to improve efficiency and to save costs, each of a plurality of oscillators may be used to jam several premium television channels in a continuous band of frequencies selected from the broadband 50-550 MHz spectrum. This technique not only reduces the amount of hardware required, but also maximizes the system flexibility. The oscillator output jamming signal frequency is periodically moved from channel to channel. Consequently, the oscillator is frequency agile and hops from jamming one premium channel frequency to the next.
Cost reduction is achieved in the systems discussed above, i.e. trap and interdiction systems, by providing shared housings outside the subscribers' premises for each of a plurality of subscriber units, for example, four such units and common circuitry associated with the several subscriber units. For example, common control circuitry is shown in FIG. 2 of U.S. Pat. No. 4,912,760. These housings are mounted out-of-doors on poles or in pedestals for serving especially suburban subscribers. Further details of such housing apparatus is also provided by U.S. Pat. No. 4,963,966. Also, indoor housings are known from so-called multiple dwelling unit systems where a cable television system supplies service to apartment buildings or condominium complexes.
In more suburban and rural environs, a single port (subscriber) unit may be provided which may, for example, be mounted to the side of an exterior of a subscriber's home.
In most if not all of these systems, however, situations arise when it is appropriate to provide a return or reverse path from a particular subscriber to a headend. The need for a reverse path has been recognized since the 1970's. Then, it was envisioned that a number of special services could be realized over a cable television distribution plant if a reverse path is provided. The services included remote utility meter reading, fire and burglar alarm, energy management, home shopping, subscriber polling or voting, educational and pay-per-view television services. However, in the 1970's and 1980's the preponderance, if not most, subscriber service providing equipment was physically located on the subscriber's premises. Consequently, there was no attention paid to a problem today of providing reverse path transmission in an off-premises subscriber equipment environment, such as exists in a CATV interdiction system.
One advance in the art of reverse path transmission from the early days of design of two way addressable cable television systems was the two way distribution amplifier. An arrangement is provided for splitting the cable television spectrum into forward and reverse frequency bands. According to a so-called sub-split distribution plant, the frequency band of 54-550 megahertz is reserved for forward, downstream transmission from the headend to the subscriber and the band from 5-30 megahertz is reserved for reverse or upstream transmission. Included in the typical distribution amplifier are diplex filters or diplexers which provide separate paths for the forward and reverse directions on one side and a path for a combined frequency spectrum on the other side.
Typically, a subscriber decoder/converter is provided with a keyboard or other data entry means through which device a subscriber may enter, for example, a home shopping selection or a pay-per-view service request. For remote meter reading, alarm, and energy management services, sensing, measurement, energy control and other devices are appropriately dispersed in a subscriber's premises. Access to the cable distribution plant is provided by a data transmission modem for both subscriber service request data, entered via the keyboard, and utility or alarm data. The data is typically transmitted as frequency shift keyed or phase shift keyed data modulated on a carrier in the 5-30 megahertz band.
As an alternative to FSK or PSK data transmission, spread spectrum techniques and alternative arrangements such as telephone return have also been proposed in cable television systems primarily because of the notorious susceptibility of the 0-30 megahertz band to noise and other interferences. In U.S. Pat. Nos. 5,109,286, 5,155,590, and 5,045,816 and U.S. patent application Ser. No. 07/612,933, filed Nov. 13, 1990, the problem of providing a reverse path data transmission system was generally described in view of the several concurrent problems which still require solution. The problems which remain unsolved include: to minimize the sophistication of subscriber premise equipment, if any, for special service applications, to effectively control off-premise service providing equipment, and to return data to the headend in a noisy, interference prone environment, the 0-30 MHz transmission band.
While arrangements as mentioned above are known for providing on-premises equipment for transmitting data over a reverse path to a headend, there remains a requirement for off-premises reverse path equipment, responsive to a minimum of on-premises equipment, for controlling off-premises service providing system equipment such as descrambling or decoding, trap or interdiction system equipment. Furthermore, there remains a requirement in the art of design of cable television equipment for off-premises reverse path equipment responsive to, and which may be shared in common by, a plurality of subscribers and thus provide a cost-effective efficient arrangement. Also, there exists a requirement in the art for off-premises reverse path equipment to provide a bi-directional transmission path to each subscriber and a bi-directional data transmission path toward the headend (relying on existing in-band or out-of-band downstream data transmission).